In microbiological research it is common practice to nurture cell colonies on growth media contained in petri dishes and transfer such cell colonies to other growth media to implement various tests. Laboratory research is facilitated by the replication and identification of the cell colonies under investigation. It is often necessary to clone these cells in order to produce sufficient quantities for a complete investigation of the cells. A process for duplicating cell colonies is widely known as replica plating.
The process of replica plating typically involves a printing-like transfer of a set of colonies from one culture surface to another culture surface or surfaces while maintaining the original pattern of the colonies. The transfer process is commonly performed by contacting cell colonies with a sterile transfer pad and then contact printing these cell colonies onto one or more additional culturing surfaces maintaining their original pattern. It is desirable in the replica plating process to use a device which is easy to operate and provides a large number of high resolution replicates.
Various replica plating tools are found in the prior art. U.S. Pat. No. 5,061,621, to Perlman, entitled REPLICA PLATING DEVICE WITH AN INTEGRAL MARKING ELEMENT, describes a device for replica plating oriented with its cell colony transfer surface face up. The cell colony transfer surface is a fabric laminated with an absorbent blotting material which is bonded to a rigid base. The base is fixed to a flat working surface by an adhesive strip and includes a set of bumper guards positioned on the side wall of the base to prevent contact of the fabric with the inside wall of the culture dish holding the cells to be replicated. This device requires that fabric be rigidly adhered to the base in order to prevent horizontal or vertical movement of the fabric surface. The fabric must be sized such that it covers the base and does not extend beyond the outer circumference of the base. A disadvantage of this device is that the fabric is adhered to base, which prevents easy removal of the fabric for washing and sterilization. Another disadvantage is the device is fixed to a flat work surface possibly requiring the operator to perform the replica plating process at one location and move the replicates to another location for investigation. Perlman does not state whether this device is capable of cleaning, sterilization and reuse or if this is a disposable device intended for only one use which may increase user expenses.
U.S. Pat. No. 4,7 17,667, to Provonchee, entitled COLONY REPLICATING DEVICE, describes a device that includes a cell colony transfer surface bonded with a water-based latex binder to a resilient backing layer. The cell colony transfer surface must be less resilient than the backing layer. A rigid cap is adhesively fixed onto the resilient backing layer. To use the device, pressure is applied to the cap which is uniformly transmitted to the backing layer and the cell colony transfer surface. A disadvantage of this device is that if the backing layer does not exhibit greater resiliency than the cell colony transfer surface then the force distributed across the cell colony transfer surface may not be even and it will not conform to the host growth medium. Another disadvantage is that the cell colony transfer surface is bonded to the backing layer and does not appear to be easily removed for washing and sterilization, and Provonchee does not state whether this device is capable of cleaning, sterilization or reuse.
U.S. Pat. No. 4,634,676, to Sapatino. entitled REPLICA PLATING DEVICE, describes a cylindrical replica plating device with a hooked skin to maintain the device in a position over the culture container controlling the movement of the device. This device has a layer of thin compressible material attached to the rigid exterior bottom surface of the device. The replica plating technique described includes a replica filter which is placed over the cells in the host medium. The downward movement of the device causes a force to be communicated through the compressible material to the replica filter. A disadvantage of this device is that the cell colonies are printed onto the replica filter, not to another growth medium. Sapatino states that preferably the device is packaged sterile and disposed of after a single use which may increase expenses to the user.
Another typical replica plating tool is disclosed in Molecular Cloning and Laboratory Manual by T. Maniatis, published by Cold Spring Harbor Laboratory, 1982, on pages 304-306. The replica plating tool resembles a hand-stamping instrument with a bottom surface and an upwardly extending post for gripping. The bottom surface includes a velvet layer to cushion the pressure of the filter paper against the cell colonies on the culture medium. Similar to the Sapatino device, the velvet layer is for cushioning only and this device only transfers cell colonies from the host medium to the filter paper. A horizontal depth stop is provided to control the depth to which the replica plating tool can penetrate. Adjustment of the horizontal depth stop is awkwardly accomplished. It is questionable as to whether this device insures sterility in the petri dish from which the cell colonies are plate printed.
The prior an demonstrates there is a need for a replica plating device that can be cleaned, sterilized and reused that is easy to operate and produces accurate replicates. The present invention incorporates several features and advantages to overcome the deficiencies of the prior art.